FORT COLLINS, Colo. (AP) Kerwynn Williams set career highs with 21 carries for 205 yards and two touchdowns in leading Utah State past Colorado State 31-19 Saturday night.

Williams, a senior, had touchdown runs of 26 and 58 yards. His only other 100-yard game came in 2010, when he gained 147 yards on 19 carries against Boise State.

The Aggies (3-1) are off to their best start since winning their first five games in 1978. They've outscored their opponents 51-0 in the first quarter and haven't given up a touchdown in the first half.

They led 17-0 at the break, and it could have been much worse.

After Williams' 26-yard TD run, the Rams (1-3) had a goal-line stand, and Utah State settled for Josh Thompson's 20-yard field goal. The Aggies needed 19 plays to cover 85 yards on their next score, capped by Chuckie Keeton's 1-yard fade pass to Matt Austin on fourth-and-goal from the 1.

Austin fumbled into the end zone in the final minute of the first half, and Colorado State cornerback Shaq Bell scooped it up.

Bell's interception in the third quarter set up Jared Roberts' second field goal, a 31-yarder that made it 17-6. Four plays later, Williams cut through the heart of the Rams' defense for his 58-yard TD.

The Rams pulled to 24-12 on Dominique Vinson's 4-yard TD catch early in the fourth quarter, but the 2-point conversion failed, and the Aggies responded with a quick 15-yard TD run by Joe Hill.

Marquise Law caught four passes for 76 yards for CSU, including a 29-yard TD toss from Garrett Grayson with 1:43 left, his first career touchdown.

For the second straight week, the Rams lost to a Western Athletic Conference team that will join them in the Mountain West next season. The Aggies snapped a four-game skid in the series.